Ingress noise inhibiting network interface device and method for cable television networks

ABSTRACT

Ingress noise from subscriber equipment is mitigated or prevented from reaching a cable television (CATV) network. All upstream signals including ingress noise are initially transmitted to the CATV network whenever their instantaneous power exceeds a threshold which typically distinguishes ingress noise from a valid upstream signal. Whenever the instantaneous power is below the threshold, ingress noise is blocked from reaching the CATV network. A gas tube surge protection device is included to resist component destruction and malfunction arising from lightning strikes and other high voltage, high current surges.

This invention relates to cable television (CATV) networks, and moreparticularly to a new and improved CATV network interface device whichinterconnects subscriber equipment at a subscriber's premises to theCATV network infrastructure. The present network interface device offersan improved capability for inhibiting the amount of undesirable ingressnoise introduced from subscriber equipment to the CATV network withoutdiminishing the information content of valid upstream signals and whileachieving use compatibility with most CATV networks without regard toupstream communication protocols or unique equipment used in the CATVnetwork.

BACKGROUND OF THE INVENTION

CATV networks supply high frequency “downstream” signals from a mainsignal distribution facility, known as a “headend,” through the CATVnetwork infrastructure to the homes and offices of subscribers to theCATV signal distribution services. The infrastructure of a typical CATVnetwork includes interconnected coaxial cables, signal splitters andcombiners, repeating amplifiers, filters, trunk lines, cable taps, droplines and other signal-conducting devices. The downstream signals aresupplied to the subscriber equipment, such as television sets, telephonesets and computers, to cause them to operate.

In addition, most CATV networks also transmit “upstream” signals fromthe subscriber equipment back to the headend of the CATV network. Forexample, a set top box allows the subscriber to select programs fordisplay on the television set. Upstream signals are sent from the settop box to the headend signal-delivering equipment that then transmitsthe selected downstream signal to the subscriber. As another example,two-way communication is essential when using a personal computerconnected through the CATV infrastructure to the public Internet. As afurther example, voice over Internet protocol (VOIP) telephone sets usethe CATV infrastructure and the public Internet as the medium fortransmitting two-way telephone conversations. Such two-way signaltransmission (upstream and downstream) is therefore an essentialrequirement for modern CATV networks.

To be effective, a CATV network must use filters and other componentswhich reduce or eliminate unwanted signals that enter the CATV networkfrom external sources. These undesirable external signals, known as“ingress noise,” have the effect of degrading valid signals, if measuresare not taken to suppress or otherwise limit the amount of ingress noisein a CATV network.

The most intense frequency of undesirable ingress noise signals is inthe frequency band of 0-15 megahertz (MHz). Valid upstream signals arewithin the frequency band of 5-42 MHz, which overlaps with the frequencyband of the most intense ingress noise. It is therefore impossible orextremely difficult to filter undesirable ingress noise from validupstream signals when the two electrical signals occupy the samefrequency band and both signals may originate at approximately the samelocation at the subscriber premises. Valid downstream signals are withinthe frequency band of 54-1000 MHz, so the ingress noise, typically inthe 0-15 MHz frequency band, is usually suppressed by filters in thedownstream frequency band.

Even though the ingress noise is typically in a frequency band differentfrom the downstream frequency band, ingress noise can still have adverseinfluence on both valid downstream and upstream signals. Ingress noisefrom individual subscribers tends to funnel together and accumulate as asubstantial underlying level of base noise on the CATV network. Validsignals must be distinguished from this base level noise, usually byamplifying the valid signals above the base noise level. A high level ofbase noise may cause signal amplifiers to clip or distort both the validdownstream and upstream signals during amplification and retransmissionof those signals, thereby reducing the information contained in thosevalid signals. A reduction in the information contained in the signalsdiminishes the quality of service experienced by the subscriber and mayeven inhibit the delivery of services to subscribers.

There are many potential sources of ingress noise in the environment ofa typical CATV network. However, the typical CATV network has arelatively high immunity to ingress noise because the CATV networkinfrastructure is essentially constructed by professionals using highquality equipment and techniques. However, the situation is usuallyconsiderably different at the subscriber premises. The quality of thesubscriber equipment, the type and integrity of the signal conductorswithin the consumer premises, the effectiveness and quality of theconnections between the subscriber equipment and the signal conductors,and the presence of many other types of electrical devices which emitnoise, such as electric motors, radios and consumer appliances, becomesources of ingress noise at the subscriber premises over which the CATVservice provider has no control.

Even though the CATV service provider may have little control over thesources of ingress noise at the subscriber premises, the CATV serviceprovider is nevertheless responsible for the quality of service, atleast from the perspective of subscribers. Therefore, different types ofingress noise inhibiting devices have been devised for use with CATVnetworks to attempt to suppress ingress noise entering the CATV networkfrom the subscriber premises.

One type of known ingress noise inhibiting device relies on downstreamsignals generated at the headend in accordance with the communicationprotocol to close an electronic switch at predetermined times and underpredetermined circumstances to establish an upstream communication pathfor valid upstream signals. Once the upstream communication isestablished, the subscriber equipment is permitted to transmit upstreamsignals in synchronization with the establishment of the path. Theupstream signals from subscriber equipment can only be communicated atthose times established by the communication protocol. At all othertimes, all upstream signals, including ingress noise, are blocked andprevented from entering the CATV network. The times when the electronicswitch is closed are established by the communication protocol, andthose time periods may not correspond with the times when the subscribermakes programming selections, desires to transmit upstream signals, oris talking during a telephone conversation, for example.

Protocol-responsive ingress noise inhibiting devices have the potentialto delay the transmission of the upstream communications, and as aresult, the response thereto, because the upstream communications pathis only established during those predetermined times set by thecommunication protocol. The times set by the communication protocol donot usually correspond with the times when the user wishes to transmitvalid upstream signals. The resulting delays are perceived by thesubscriber as deficient responsiveness and a reduction in the quality ofservice. Furthermore, since the time intervals for transmitting upstreamsignals is preestablished by the communication protocol, the closedelectronic switch permits ingress noise to enter the CATV network duringthose times when there are no subscriber upstream signals to transmit,thereby allowing ingress noise to enter the CATV network.

A further difficulty with such protocol-responsive ingress noiseinhibiting devices is that they are specifically useful only in thosetypes of CATV networks which require a specific communication protocol.Because not all CATV networks operate on the same basis,protocol-controlled ingress noise inhibiting devices do not have wideapplicability to a variety of different types of CATV networks and CATVservice providers. In addition, synchronizing the subscriber equipmentto the CATV network protocol requires specialized equipment.

A related type of ingress noise inhibiting device permits upstreamcommunications in only one or more narrow band pass frequencies, forexample at 11 and/or 26 MHz. Filters are employed to block any ingressnoise within the other ranges of the 5-42 MHz upstream frequency bandand the 0-15 MHz typical ingress noise frequency band. Although suchbandpass ingress noise inhibiting devices are effective in suppressingthe ingress noise outside of the bandpass frequencies, ingress noise isstill able to enter the CATV network at the selected bandpass upstreamfrequencies. Further, the use of such narrow frequency bandpass ingressnoise inhibiting devices is applicable only to those types of CATVnetworks which limit the frequency of valid upstream signals topreselected frequency bands. The use of preselected upstream frequencybands for valid upstream signals is not universally applicable to avariety of different types of CATV networks and CATV service providers.

Another type of ingress noise inhibiting device is one which responds toan auxiliary out-of-band signal to close an electronic switch andestablish an upstream communication path. For example, the auxiliaryout-of-band signal may be a 1 MHz tone, which falls outside of theupstream frequency band. The subscriber equipment generates thisout-of-band signal whenever it wishes to transmit an upstreamcommunication. The ingress noise inhibiting device responds to theout-of-band signal and closes the electronic switch to establish thecommunication path for the upstream signal in the 5-42 MHz frequencyband. Typically, the out-of-band signal remains present while theupstream signal is transmitted. When the out-of-band signal is notgenerated, the electronic switch opens to block the communication path,thereby preventing ingress noise from entering the CATV network. Suchingress noise inhibiting devices require the subscriber equipment andset-top boxes to have the additional functionality of generating,recognizing and responding to the out-of-band signal. Such equipment isnot common, and adds to the cost and difficulty of the equipment supportoperations of the CATV service provider. Furthermore, the ingress noiseinhibiting device also requires additional components to function in afrequency band different from the normal 5-42 MHz upstream frequencyband in which other components operate. Lastly, ingress noise in theout-of-band frequency range can also cause the electronic switch toclose and establish the upstream communication path when there is novalid upstream signal to transmit, thereby admitting ingress noise on tothe CATV network.

Other types of ingress noise inhibiting devices attempt to distinguishingress noise from valid upstream signals, on the basis ofcharacteristic differences in the ingress noise signals and the validupstream signals. Ingress noise is characterized by erratic amplitudeand timing variations, while valid upstream signals are characterized byregular amplitude and consistent timing characteristics. Valid upstreamsignals are frequently transmitted in the form of packets, which aredefined by the presence and absence of high-frequency pulses thatconstitute bits of a digital signal. The typical packet includes apreamble with a series of high-frequency pulses representing digitalbits which define the start of the packet. Certain packet-responsiveingress noise inhibiting devices attempt to recognize the preamble, andin response, close an electronic switch to establish a pathway for thevalid upstream signal. Distinguishing the preamble requires time torecognize its regular timing and amplitude characteristics. The amountof time available to perform such recognition may not always beadequate, particularly when the high-frequency pulses of the preambleare of low or moderate strength. Under those circumstances, the upstreamcommunication path may not be established quickly enough to transmit thebody of substantive information carried by the packet, thereby resultingin loss of some of the information and the perception of a diminishedquality of service. Not all CATV networks operate on a digital packetcommunication protocol, so the applicability of packet-responsiveingress noise inhibiting devices is not universal.

Another difficulty arising from some known ingress noise inhibitingdevices involves attempting to switch filters in and out of electricalconnection to establish the upstream communication path and to suppressthe ingress noise when the upstream communication path is notestablished. Switching filters in and out of circuit connection requiresa finite amount of time for the energy storage inductors and capacitorsof such filters to store the necessary energy and to achieve stabilizedoperability to perform filtering. Of course, the time required to storethe energy, achieve stability and commence filtering the signals mayalso result in truncating or diminishing the information content of theupstream signals.

Still another type of ingress noise inhibiting device attempts todistinguish between spurious ingress noise and valid upstream signals onthe basis of their energy content. Such devices function by integratingthe power of the signals over time to arrive at an energy value. Theassumption is that the power of valid upstream signals, when integrated,will represent an energy content sufficiently greater than theintegrated power or energy of spurious ingress noise signals, becausevalid upstream signals have sustained energy while spurious noisesignals have erratic low energy. The sustained length of valid upstreamsignals integrates to recognizable energy level, while the short anderratic length of ingress noise integrates to a much lesser energylevel. After the time period required for integrating the power intoenergy, the energy level is compared to a predetermined threshold energylevel which has been selected to represent a valid upstream signal. Ifthe energy level exceeds the predetermined threshold energy level, anelectronic switch is closed to establish the upstream communicationpath. If the integration of the power results in an energy level whichis less than the predetermined threshold energy level, it is assumedthat the signal is ingress noise, and the electronic switch remains opento prevent any signals from reaching the CATV network.

To integrate the power level of upstream signals into energy, a timedelay is required before valid upstream signals can be transmitted tothe CATV network. This delay in transmitting valid upstream signalspresents the possibility that some of the valid upstream signal will belost or truncated before the upstream communication path is established.

SUMMARY OF THE INVENTION

The CATV network interface device and method of this invention areeffective in mitigating ingress noise over the entire 5-42 MHz upstreamfrequency band of a CATV network, and do so while transmitting validupstream signals almost instantaneously to avoid loss of informationcontent. The valid upstream signals are transmitted without requiring atime delay sufficient to determine energy content. Consequently, validupstream signals are transmitted almost immediately to the CATV networkafter the subscriber equipment generates those signals. The almostinstantaneous transmission of valid upstream signals avoids the risk ofloss of information content. The present device and method is notlimited in its applicability or use to any particular type of CATVnetwork or any particular type of communication protocol used on a CATVnetwork. The present ingress noise inhibiting network interface deviceand method do not require synchronization with CATV networkcommunication protocol or require special functionality in subscriberequipment to synchronize valid upstream signals with the CATV networkcommunication protocol. No out-of-band signaling or functionality isrequired to implement the present invention. Upon termination of thevalid upstream signal, the present device and method quickly revert to acondition which effectively blocks ingress noise from the CATV network.No filters are switched into or out of electrical connection. Whenblocking ingress noise from the CATV network, the connections to theCATV network and to the subscriber equipment are terminated intocharacteristic impedances to minimize reflected signals that detractfrom valid signals.

In accordance with these and other features, one aspect of the presentinvention involves a network interface device which has an upstreamnoise mitigation circuit that mitigates the ingress of noise fromsubscriber equipment into a cable television (CATV) network. The CATVnetwork transmits downstream signals in a first frequency band from aheadend to the subscriber equipment and transmits upstream signals in asecond different frequency band from the subscriber equipment to theheadend. The ingress noise mitigation circuit comprises a downstreamfilter which filters downstream signals before delivery to thesubscriber equipment, and an upstream filter which filters upstreamsignals before delivery to the CATV network. A detector determines aninstantaneous level of power of the upstream signals. A thresholdcircuit establishes a predetermined threshold power level whichdistinguishes typical ingress noise from valid upstream signals. Acomparator compares the instantaneous power level of the upstream signalwith the threshold power level and asserts a trigger signal when theinstantaneous power level exceeds the threshold power level. A switch isconnected to the upstream filter and terminates the upstream filter in acharacteristic impedance to block upstream signals and to prevent orminimize signal reflection when in a normal position. The switchconducts the upstream signals from the subscriber equipment to the CATVnetwork when in an activated position. The switch assumes the activatedposition when the instantaneous power level exceeds the threshold powerlevel, as represented by the assertion of the trigger signal, andassumes the normal position under usual circumstances and when theinstantaneous power level is less than the threshold power level,represented by the de-assertion of the trigger signal. By activating theswitch immediately after the instantaneous power content of the upstreamsignal exceeds the threshold power level, there is little possibility oropportunity for the information contained in the upstream signals to belost, truncated or diminished.

Other aspects of the network interface device involve a timer which isoperative to maintain the switch activated for a predetermined timeperiod after the instantaneous power level exceeds the threshold powerlevel and which is operative to return the switch to the normal positionafter expiration of a predetermined time period after the switch isactivated. The predetermined time is sufficient to transmit a singlevalid maximum-length upstream signal. The continued presence of energyfrom multiple valid sequential upstream signals maintains the switch inthe activated position to permit transmission of those signals. Shouldingress noise have an instantaneous power level sufficient to exceed thethreshold power level, the switch will quickly resume the normalposition and prevent further transmission of the ingress noise after theingress noise dissipates.

Additional aspects of the network interface device involve first andsecond upstream filters which filter the upstream signals beforedelivery to the CATV network, and first and second switches connected tothe first and second upstream filters. The first and second switchesassume activated positions in response to the instantaneous powercontent exceeding the threshold power level and assume normal positionsin response to the instantaneous power content remaining below thethreshold power level. In the normal positions, the two switchesterminate the filters through characteristic impedances to preventingress noise from the subscriber equipment from reaching the CATVnetwork. In the activated positions, the two switches conduct theupstream signals through the first and second upstream filters.

Another aspect of the present invention is a network interface devicewhich includes a gas tube surge protection device. The gas tube surgeprotection device shunts high voltage and high current surges, such asthose arising from lightning, from CATV network components and thesubscriber equipment.

A method of mitigating upstream noise originating from subscriberequipment is a further aspect of the present invention. The methodinvolves filtering upstream signals including upstream noise to confinethe frequency of the upstream signals to an upstream frequency band,determining an instantaneous power content of the upstream signals,establishing a threshold power level which typically distinguishesingress noise from valid upstream signals, comparing the instantaneouspower content of the upstream signals to the threshold power level,blocking the filtered upstream signals from the CATV network when theinstantaneous power content is less than the threshold power level, andconducting the filtered upstream signals to the CATV network when theinstantaneous power content is at least equal to the threshold powerlevel.

Other features of the method involve conducting upstream signals to theCATV network for a predetermined time period after the instantaneouspower content exceeds the threshold power level. The instantaneous powercontent is integrated over a predetermined integration time to arrive atan integration value. If the integration value is less than apredetermined threshold energy level, thereby signifying ingress noise,the upstream communication path is blocked to prevent the ingress noisefrom reaching CATV network after the predetermined integration time haselapsed. If the integration value is greater than the predeterminedthreshold energy level, thereby signifying the presence of a validupstream signal, the upstream communication path is maintained for thetime duration of a single valid maximum-length upstream signal. If theintegration value is greater than the predetermined threshold energylevel, thereby signifying the presence of a valid upstream signal, andthe instantaneous power of the valid upstream signal continues after thetime duration of a maximum-length upstream signal, the valid upstreamsignal is constituted by a sequence of multiple valid upstream signals.In this circumstance, the upstream communication path is maintained forthe time duration of the multiple valid upstream signals. In therespective cases of a single valid upstream signal or multiplesequential valid upstream signals, maintaining the upstreamcommunication path for the duration of a single maximum-length upstreamsignal assures or for the duration of the multiple sequential validupstream signals assures that the information contained in the validupstream signals will be fully and accurately transmitted withouttruncation or other loss of information. After the time duration of asingle valid maximum-length upstream signal or the time duration of asequence of multiple valid upstream signals, the upstream communicationpath is terminated to block ingress noise from entering the CATVnetwork.

Other features and aspects of the invention, and a more completeappreciation of the present invention, as well as the manner in whichthe present invention achieves the above and other improvements, can beobtained by reference to the following detailed description of presentlypreferred embodiments taken in connection with the accompanyingdrawings, which are briefly summarized below, and by reference to theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a network interface device whichincorporates the present invention and a block diagram of subscriberequipment shown connected to a CATV network through the networkinterface device located at a subscriber's premises.

FIG. 2 is a block diagram of portions of a typical CATV network, withmultiple network interface devices of the type shown in FIG. 1 connectedby drop cables to cable taps, as well as other aspects of the CATVnetwork.

FIG. 3 is a block diagram of basic functional components within thenetwork interface device shown in FIG. 1.

FIGS. 4, 5 and 6 contain multiple waveform diagrams on a common timeaxis, illustrating the functional features of an upstream noisemitigation circuit of the network interface device shown in FIG. 3.

FIG. 7 is a block diagram of basic functional components of an upstreamnoise mitigation circuit which is an alternative to that shown in FIG.3.

FIGS. 8, 9 and 10 contain multiple waveform diagrams on a common timeaxis, illustrating the functional features of the upstream noisemitigation circuit shown in FIG. 7.

DETAILED DESCRIPTION

A network interface device 10 which incorporates the present inventionis shown in FIG. 1. The network interface device 10 includes a housing12 which encloses internal electronic circuit components (shown in FIGS.3 and 7). A mounting flange 14 surrounds the housing 12, and holes 16 inthe flange 14 allow attachment of the interface device 10 to a supportstructure at a subscriber's premises 18.

The interface device 10 is connected to a conventional CATV network 20,which is shown in a typical topology in FIG. 2. Downstream signals 22originate from programming sources at a headend 24 of the CATV network20, and are conducted to the interface device 10 in a sequential paththrough a main trunk cable 26, a signal splitter/combiner 28, secondarytrunk cables 30, another signal splitter/combiner 32, distribution cablebranches 34, cable taps 36, and drop cables 38. Upstream signals 40 aredelivered from the network interface device 10 to the CATV network 20,and are conducted to the headend 24 in a reverse sequential path.Interspersed at appropriate locations within the topology of the CATVnetwork 20 are conventional repeater amplifiers 42, which amplify boththe downstream signals 22 and the upstream signals 40. Conventionalrepeater amplifiers may also be included in the cable taps 36. The cabletaps 36 and signal splitter/combiners 28 and 32 divide a single inputdownstream signal into separate downstream signals, and combine multipleupstream signals into a single upstream signal.

The network interface device 10 receives the downstream signals 22 fromthe CATV network 20 at a network connection port 44. The downstreamsignals 22 are either passive or active. Passive downstream signals arethose signals which are conducted through the interface device 10without amplification, enhancement, modification or other substantialconditioning. The passive downstream signals are delivered from apassive port 45 to passive subscriber equipment, such as a voice modem46 connected to a telephone set 48, or an embedded multimedia networkinterface device (EMTA, not shown), located at the subscriber premises18. Active downstream signals are those signals which are amplified,filtered, modified, enhanced or otherwise conditioned by power-consumingactive electronic circuit components within the interface device 10. Theconditioned active downstream signals are divided into multiple copiesand delivered from a plurality of active ports 50, 52, 54 and 56 toactive subscriber equipment located at the subscriber premises 18, suchas television (TV) sets and/or data modems 58, 60, 62 and 64. Othersubscriber equipment, such as data processing devices or computers, isconnected to the data modems.

The equipment at the subscriber premises 18 typically generates upstreamsignals 40 (FIG. 2) to the network interface device 10 for delivery tothe CATV network 20. The upstream signals 40 may be either active orpassive upstream signals generated by the subscriber equipment connectedto the active and passive ports 45, 50, 52, 54 and 56. For example, oneor more of the TV sets 58, 60, 62 and 64 may have conventional set topboxes (not shown) associated with them to allow the subscriber/viewer tomake programming and viewing selections. Of course, any computers (notshown) connected to the data modems 58, 60, 62 and 64 typicallycommunicate upstream signals. The telephone set 48 and the voice modem46, or the EMTA (not shown), also generate upstream signals as a part oftheir typical functionality.

Electrical power for the network interface device 10 is supplied from aconventional DC power supply 66 connected to a dedicated power inputport 68. Alternatively, electrical power can be supplied through aconventional power inserter (also shown at 58) that is connected to theport 50. The power inserter allows relatively low voltage DC power to beconducted through the same port 50 that also conducts high-frequencysignals. Use of a conventional power inserter connected to one of theports, e.g. port 50, eliminates the need for a separate dedicated powersupply port 68, or provides an alternative port through which electricalpower can also be applied. The power supply 66 or the power suppliedfrom the port 50 is typically derived from a conventional wall outlet(not shown) within the subscriber premises 18.

The ports 44, 45, 50, 52, 54, 56 and 68 are each preferably formed by aconventional female coaxial cable connector which is mechanicallyconnected to the housing 12 and which is electrically connected tointernal components of the interface device 10. Coaxial cables from thesubscriber equipment and the drop cables 38 (FIG. 2) are connected tothe interface device 10 by mechanically connecting the correspondingmating male coaxial cable connector (not shown) on these coaxial cablesto the female coaxial cable connectors forming the ports 44, 45, 50, 52,54, 56 and 68.

The internal circuit components of one embodiment of the networkinterface device 10 are shown in FIG. 3. Those internal circuitcomponents include a conventional bi-directional signalsplitter/combiner 70 which separates the input downstream signals 22from the CATV network 20 at the cable port 44 into passive downstreamsignals 72 and active downstream signals 74 within the network interfacedevice 10. The passive downstream signals 72 are conducted directlythrough the passive port 45 to the passive subscriber equipment 46 and48. Passive upstream signals 76 created by the passive subscriberequipment 46 and 48 are conducted through the passive port 45 directlyto the signal splitter/combiner 70 to become upstream signals 40 in theCATV network 20. The direct signal conductivity path for the passivesignals in the network interface device 10 avoids subjecting the passivesignals to potentially adverse influences from electronic componentsthat might fail or malfunction, thereby enhancing the reliability of thepassive communications without increasing the risk of failure. Passivecommunications are intended to be as reliable as possible since they maybe used in emergency and critical circumstances.

The active downstream signals 74 are conducted to active circuitry 78,where the active downstream signals 74 are amplified, filtered,modified, enhanced or otherwise conditioned before delivery through theactive ports 50, 52, 54 and 56 to the subscriber equipment 58, 60, 62and 64. Active upstream signals 80 are created by the subscriberequipment 58, 60, 62 and 64, and also pass through the active circuitry78, where those signals are also conditioned or otherwise modified orenhanced before being combined at the signal splitter/combiner 70 tobecome network upstream signals 40 in the CATV network 20.

The circuit components of the active circuitry 78 receive power from thepower supply 66 connected at port 68 or through the power inserter 58(FIG. 1) connected at port 50. A conventional power-signal divider 82separates the high-frequency active downstream and upstream signals 74and 80 at port 50 from the DC power at port 50. The divider 82 conductsthe active signals 74 and 80 from and to high-frequency signalconductivity paths within the active circuitry 78, while simultaneouslyconducting the DC power to the active circuitry 78 for use by itselectrical power consuming components. Electrical power from thededicated power input port 68 is also conducted to the power consumingcircuit components of the active circuitry 78.

The components of the active circuitry 78 which conduct the downstreamactive signals 74 include first and second analog downstream filters 84and 86 that are connected in series by a linear amplifier 88. Thedownstream filters 84 and 86 filter the downstream signals 74 in thedownstream 54-1000 MHz frequency band. The linear amplifier 88amplifies, modifies or enhances the downstream signals 74, and inconjunction with the filters 84 and 86, conditions the downstreamsignals 74. The downstream signals 74 are thereafter connected throughconventional signal splitter/combiners 90, 92 and 94 before thosedownstream signals 74 are delivered through the active ports 50, 52, 54and 56 to the subscriber equipment 58, 60, 62 and 64.

The active upstream signals 80 created by the subscriber equipment 58,60, 62 and 64 are conducted through the active ports 50, 52, 54 and 56to an upstream noise mitigating circuit 100. The upstream noisemitigation circuit 100 transfers valid active upstream signals 80 fromthe subscriber equipment 58, 60, 62 and 64 through the network interfacedevice 10 to the CATV network 20 as upstream signals 40. These functionsare accomplished as described below.

Valid upstream signals from the subscriber equipment 58, 60, 62 and 64are conducted through the signal splitter/combiners 92, 94 and 90 tobecome active upstream signals 80. The upstream signals 80 are appliedto a first upstream signal bandpass filter 102. Because the downstreamsignal filter 86 passes signals only in the 54-1000 MHz band, validupstream signals 80 in the frequency band of 5-42 MHz are blocked by thedownstream signal filter 86 and diverted through the upstream signalfilter 102. The first upstream signal filter 102 preferably passessignals in the valid upstream signal frequency range of 5-42 MHz.Typical ingress noise falls within most intensely within the frequencyrange of 0-15 MHz, so the first upstream filter 102 has the capabilityof removing ingress noise at the low frequencies in the range of 0-5MHz. However, ingress noise in the range of 5-15 MHz will be conductedby the upstream signal filter 102.

To mitigate or prevent ingress noise upstream signals from entering theCATV network 20 from the network interface device 10, ingress noisesignals conducted through the first upstream filter 102 are isolated bya first radio frequency (RF) single pole double throw (SPDT) electronicswitch 104 and terminated to ground through a termination resistor 103.The termination resistor 103 is connected to one terminal of the firstelectronic switch 104. Signals from the first upstream signal filter 102are conducted through a conventional directional coupler 105 to andthrough the switch 104 to the termination resistor 103 while the firstelectronic switch 104 is in a normal position, shown in FIG. 3. Allsignals conducted through the first upstream signal filter 102 areterminated through the termination resistor 103, and are therebyprevented from entering the CATV network 20, while the first switch 104is in its normal position.

The first electronic switch 104 changes to an alternate activatedposition (not shown in FIG. 3) upon the instantaneous power of thesignals conducted through the filter 102 reaching a magnitude indicativeof a valid upstream signal from the subscriber equipment 58, 60, 62 or64. To distinguish relatively low power ingress noise from therelatively higher power of a valid upstream signal, the instantaneousmagnitude of the power of the signals passing through the upstreamfilter 102 is detected and evaluated. The coupler 105 delivers a signal106 which is typically 10 dB lower in power than the signal passingthrough the coupler 105 to the switch 104.

The signal 106 from the coupler 105 is conducted to an input terminal ofa conventional log amplifier detector 108. The log amplifier detector108 operates on an inverse logarithmic basis to convert theinstantaneous magnitude of power of the signal 106 to a DC voltageoutput signal 110. By operating on an inverse logarithmic basis, thetypical decibel power of the input signal 106 is converted into a linearDC voltage output signal 110 whose magnitude is inversely related to theinstantaneous input power. This logarithmic conversion allows the logamplifier detector 108 to function as an instantaneous demodulatingpower detector whose output DC voltage signal is inversely proportionalto the logarithm of the input power. A log amp detector 108 which issatisfactory for use in the present invention is part number AD 8319available from Analog Devices of Norwood Mass., USA. The DC voltageoutput signal 110 therefore represents the inverse of the instantaneouspower of the upstream signal 80 conducted through the directionalcoupler 105.

The DC voltage output signal 110 from the log amp detector 108 isapplied to a negative input terminal of a comparator 112. A thresholdsignal 114 is applied to the positive input terminal of the comparator112. The threshold signal 114 is derived from a resistor divider networksuch as a potentiometer 116 and a resistor 118 connected in series, orfrom another voltage source. Adjustment of the value of thepotentiometer 116 adjusts the magnitude of the threshold signal 114. Theadjustment of the threshold signal 114 establishes the level where antrigger signal 120 from the comparator 112 switches from a logic lowlevel to a logic high level.

The magnitude of the DC voltage output signal 110 from the log ampdetector 108 is inversely related to the magnitude of the instantaneouspower of the upstream signal represented by signal 106. That is, whenthe magnitude of the upstream signal 106 is relatively large, the DCvoltage output signal 110 from the log amp detector 108 is relativelysmall, and vice versa. Because of this inverse relationship, the DCvoltage output signal 110 is applied to the negative input terminal ofthe comparator 112, and the threshold signal 114 is applied to thepositive input terminal of the comparator 112. Applying the two inputsignals in this manner causes the comparator 112 to supply a logic hightrigger signal 120 whenever the magnitude of the instantaneous power ofthe upstream signal exceeds a predetermined threshold power levelrepresentative of a valid upstream signal. Conversely, when the DCvoltage output signal 110 is greater than the signal 114, the triggersignal 120 from the comparator 112 is at a logic low level. When the DCvoltage output signal 110 is less than the signal 114, the triggersignal 120 from the comparator is at a logic high level. The logic highlevel of the signal 120 therefore represents the condition where theinstantaneous power of the upstream signal exceeds the predeterminedthreshold power level established by the signal 114.

Upon sensing that the instantaneous power content of an upstream signalexceeds the level represented by the predetermined threshold powerlevel, the upstream signal is immediately transmitted or passed to theCATV network 20 as a network upstream signal 40. Upstream signals whichdo not meet the threshold power level are considered ingress noise.Ingress noise signals are isolated from the CATV network 20 by theswitches 104 and 130, while incident upstream signals 80 aresimultaneously terminated to ground through the termination resistor103. The functions of passing upstream signals to the CATV network andterminating upstream signals to ground are accomplished in response tothe logic level of the trigger signal 120 from the comparator 112.

When instantaneous power content of an upstream signal exceeds thethreshold power level, the resulting logic high signal 120 from thecomparator 112 triggers a one-shot timer 122. Simultaneously, the logichigh signal 120 is applied to an input terminal of an OR gate 124. TheOR gate 124 responds by applying a logic high control signal 126 to thecontrol terminals of the first SPDT RF electronic switch 104 and asecond SPDT RF electronic switch 130. The electronic switches 104 and130 normally occupy the positions shown in FIG. 3. Upon the assertion oflogic high control signal 126, the switches 104 and 130 immediatelychange from their normal positions (shown in FIG. 3) to their oppositeactivated positions (not shown). The activated positions of the switches104 and 130 establish a direct connection over conductor 132 between theswitches 104 and 130. Since the electronic switches 104 and 130 switchwith radio frequency speed, the switches 104 and 130 assume theactivated position almost instantaneously in response to the assertionof the control signal 126.

The activated positions of the switches 104 and 130 conduct the upstreamsignal 80 from the first upstream signal filter 102 through theconductor 132 to a second upstream signal filter 134. Both filters 102and 134 suppress frequencies other than those in the frequency band of5-42 MHz. The valid upstream signal flows from the second upstreamfilter 134 through the signal splitter/combiner 70 into the cablenetwork 20 as the network upstream signal 40. Terminating resistors 103and 190 are connected to the filters 102 and 134 when the switches 104and 130 are in their normal positions, and the filters 102 and 134 areconnected together over the conductor 132 when the switches 104 and 130are in their activated positions.

Valid upstream signals are conducted to the CATV network almostinstantaneously when the instantaneous power level of the upstreamsignals exceeds the threshold power level. By responding almostinstantaneously when the threshold power level is exceeded, the chancesare minimized that the information contained in the valid upstreamsignal will be lost, as might be the case if the power of the upstreamsignal had to be integrated over a time period before a determination ofa valid upstream signal could be made on the basis of energy content.Such integration raises the possibility that some of the information ofthe upstream signal will be lost and not transferred upstream. Incontrast, no integration of the power of the upstream signal over aselected time period is required in the upstream noise mitigationcircuit 100. By almost instantaneously transmitting upstream signalswhich have a power content that exceeds the predetermined thresholdpower level, the integrity of the information contained in the upstreamsignal is better preserved.

Once the switches 104 and 130 have been moved to the activated positionwhich directly connects the first and second upstream signal filters 102and 134 through the conductor 132, the switches 104 and 130 aremaintained in this activated position for a time determined by theone-shot timer 122. When triggered by the logic high signal 120, theone-shot timer 122 immediately supplies a logic high output signal 136to the OR gate 124. Either logic high signal 120 or 136 causes the ORgate 124 to supply the logic high control signal 126. If the power levelof the upstream signal falls below the level of the threshold signal114, the signal 120 immediately assumes a logic low level. However, theone-shot timer 122 will continue to deliver the logic high output signal136 for the time duration of its internal time constant.

The internal time constant of the one-shot timer 122 is equal to theamount of time to transmit a single valid upstream signal packet of themaximum time duration permitted by the signaling protocol, plus a slightadditional amount of time to account for inherent tolerances in thecomponents and the timing of the one-shot timer 122. In this manner, theone-shot timer 122 ensures that the switches 104 and 130 assume theiractivated positions for a long enough time to conduct all single validupstream signals, including a maximum-length valid upstream signal orpacket.

The situation just described is illustrated by the waveform diagramsshown in FIG. 4, taken in connection with FIG. 3. The signal 106represents a single valid upstream packet of the permitted maximum timeduration whose detection by the log amp detector 108 produces the logichigh trigger signal 120. The signal 120 assumes the logic high level attime point 138, triggering the one-shot timer 122 and causing the outputsignal 136 to be asserted at the same time point 138. The control signal126 from the OR gate 124 immediately assumes a logic high level at timepoint 138. The electronic switches 104 and 130 assume their activatedpositions for the duration of the logic high control signal 126. At timepoint 139, the maximum time duration of a single valid upstream packetor signal ends, and the instantaneous power represented by that signalfalls below the threshold power level represented by the thresholdsignal 114. The signal 120 assumes a logic low level. Since the timeconstant of one-shot timer 122 is established to slightly exceed themaximum time duration of a single valid upstream packet or signal, thelogic high signal 136 will continue to time point 140. When the signal136 assumes a logic low level after the one-shot timer 122 times out attime point 140, the control signal 126 from the OR gate 124simultaneously assumes a logic low level. As a result, the controlsignal 126 is longer in duration than signal 120. When the controlsignal 126 assumes the low logic level at time point 140, the electronicswitches 104 and 130 assume their normal positions to conduct anyupstream signals to the termination resistor 103, thereby terminatingthose signals to ground and preventing the further upstream signals fromreaching the CATV network.

For multiple valid upstream signal packets which are consecutivelytransmitted without a substantial time interval separating the multiplesequential upstream packets, the one-shot timer 122 will time out beforethe valid upstream signal transmission terminates. However, thecontinuous instantaneous power of the multiple sequential valid upstreamsignal packets will continue to exceed the threshold power level for theduration of the multiple sequential signal packets, thereby causing thecomparator 112 to continue to assert the logic high trigger signal 120to the OR gate 124 for the duration of the multiple sequential signalpackets. The continued application of the logic high signal 120 causesthe OR gate 124 to assert the logic high control signal 126 beyond thetime when the one-shot timer 122 times out. The two upstream signalfilters 102 and 134 remain connected by the switches 104 and 130 intheir activated positions, and thereby conduct the multiple sequentialupstream signal packets to assure that the full information representedby the multiple sequential signal packets is not truncated or lost bypremature termination of those signals. At the termination of suchmultiple upstream signal packets, the signal power no longer exceeds thethreshold signal 114, and the switches 104 and 130 immediately assumetheir normal positions, thereby preventing any ingress noise fromentering the CATV network 20 after the longer or multiple sequentialvalid upstream packets have been transmitted.

The situation just described is illustrated by the waveform diagramsshown in FIG. 5, taken in conjunction with FIG. 3. The signal 106represents three, for example, sequential valid upstream packets orsignals. The trigger signal 120 assumes the logic high level at timepoint 142 in response to recognizing the first of the sequential validupstream packets. The one-shot timer 122 is triggered and causes theoutput signal 136 to be asserted at time point 142. The control signal126 from the OR gate 124 also assumes a logic high level at time point142 in response to the assertion of the control signal 136. Theelectronic switches 104 and 130 assume their activated positions inresponse to the logic high control signal 126. At time point 140, theone-shot timer 122 times out, causing its output signal 136 to assume alogic low level. However, the instantaneous power level from themultiple sequential upstream signal packets continues to exceed thethreshold power level, until the sequence of multiple upstream signalpackets terminates at time point 146. So long as the signal 120 is at alogic high level, the control signal 126 from the OR gate 124 causes theelectronic switches 104 and 130 to remain in the activated position,conducting the multiple sequential valid upstream signal packets to theCATV network 20. Once the sequence of multiple valid upstream signalpackets has been transmitted, which occurs at time point 146, theabsence of any further valid upstream signal causes the instantaneouspower level to fall below the threshold power level, and the signals 120and 126 assume a logic low level. The electronic switches 104 and 130respond by assuming their normal positions to prevent the furthertransmission of upstream signals to the CATV network.

If the instantaneous power of ingress noise exceeds the threshold powerlevel, the electronic switches 104 and 130 assume their activatedpositions, as can be understood from FIG. 3. An unusually high and shortduration power level of ingress noise can cause this situation. Underthat circumstance, the trigger signal 120 assumes a logic high level,and the one-shot timer 136 is triggered and asserts the output signal136. The electronic switches 104 and 130 assume their activatedpositions, allowing the ingress noise to pass through the upstreamfilters 102 and 134. Until the one-shot timer 122 times out, ingressnoise will be allowed to enter the CATV network 20. The effect of thisingress noise is minimized by the time constant of the one-shot timer122 extending only for the maximum time duration of the longest singlevalid upstream signal packet permitted under the communication protocol.

The response to ingress noise having instantaneous power that exceedsthe threshold is illustrated by the waveform diagrams shown in FIG. 6,taken in connection with FIG. 3. The ingress noise signal is shown at106. Because the instantaneous power of the ingress noise exceeds thethreshold, a logic high trigger signal 120 is asserted from thecomparator 112 at time point 148, thereby triggering the one-shot timer122 and causing the signal 136 to be asserted at the same time point148. The logic high signal 136 causes the OR gate 124 to assert thelogic high control signal 126 at time point 148. The electronic switches104 and 130 assume their activated positions for the duration of thehigh level of the control signal 126. At time point 150, theinstantaneous power from the ingress noise falls below the thresholdpower level, causing the comparator 112 to assert a logic low triggersignal 120. However, the one-shot timer 122 has not timed out andcontinues to deliver the logic high signal 136 for the time duration ofits time constant, until time point 140. The control signal 126 from theOR gate 124 transitions to a logic low level at time point 140 when theone-shot timer 122 times out, causing the electronic switches 104 and130 (FIG. 3) to assume their normal positions. The electronic switch 104connects the termination resistor 103 to terminate any further upstreamsignals to ground and thereby prevent any further transfer of upstreamsignals to the CATV network.

An alternative form 160 of the upstream noise mitigation circuit, shownin FIG. 7, reduces the amount of time that ingress noise may beconducted to the CATV network 20 after the initial instantaneous powerof the ingress noise is sufficient to exceed the threshold power level,compared to the response of the circuit 100 (FIG. 3). The upstream noisemitigation circuit 160 shown in FIG. 7 includes many of the samecomponents as the upstream noise mitigation circuit 100 (FIG. 3), andthose same components function in the manner previously described.

In response to the instantaneous power of the ingress noise exceedingthe threshold power level, represented by signal 114, the comparator 112supplies the logic high trigger signal 120, in the manner previouslydescribed. The logic high trigger signal 120 is applied to a one-shottimer 162, to the input terminal of a SPDT RF electronic switch 164, toa second one-shot timer 168, and to the set terminal of a set-resetlatch 172. In response to the logic high signal 120, the first one-shottimer 162 triggers and supplies an output signal 166. Simultaneously,the second one-shot timer 168 is triggered and supplies a signal 170.The latch 172 is immediately set in response to the logic high triggersignal 120 and supplies the control signal 126 to the RF electronicswitches 104 and 130, causing them to switch to their activatedpositions and establish the upstream signal communication path forconducting upstream signals through the upstream signal filters 102 and134. In this manner, the noise mitigation circuit 160 responds almostinstantaneously to the instantaneous power of the upstream signalexceeding the threshold to immediately conduct the upstream signal tothe CATV network without delay and without the risk of diminishing orlosing some of the information contained in the upstream signal. In thisregard, the upstream noise mitigation circuit 160 (FIG. 7) is similar ininitial response to the upstream noise mitigation circuit 100 (FIG. 3).However, the upstream noise mitigation circuit 160 has the capability ofmore quickly closing the upstream communication path through theswitches 104 and 130 when the upstream communication path was initiallyestablished in response to ingress noise.

The rapid closure of the upstream communication path in response toingress noise is accomplished by integrating the signal 120 for apredetermined time established by the time constant of the one-shottimer 162. The logic high trigger signal 120 represents the power of theingress noise exceeding the predetermined threshold power level.Integrating the logic high trigger signal 120 results in a value whichrepresents energy above the threshold power level for the time durationof integration. Integration occurs over the time that the signal 166 isasserted by the one-shot timer 162. If the amount of power integratedduring this time, i.e. energy, is not sufficient to confirm a validupstream signal with continuous sustained instantaneous power, theswitches 104 and 130 are moved to their normal positions, therebyterminating the upstream communication path. Since ingress noisegenerally does not contain significant sustained energy even though aninitial burst of the ingress noise may have sufficient instantaneouspower to exceed the threshold, the upstream communication path isquickly closed in a typical ingress noise situation.

Integrating the power represented by the threshold power level isaccomplished by an integration circuit 179. The integration circuit 179includes an operational amplifier 176. The positive input terminal ofthe operational amplifier 176 is connected to ground reference. Acapacitor 178 is connected between the negative input terminal and theoutput terminal of the operational amplifier 176. The negative inputterminal of the operational amplifier 176 is the input point for signalsto the integration circuit 179.

Prior to commencement of integration, the switch 164 is in its normalposition shown in FIG. 7. In the normal position of the switch 164, apositive voltage signal 171 is conducted from a power supply source 175to a resistor 174 which is connected to the negative input terminal ofan operational amplifier 176. Applying the positive voltage to thenegative input terminal of the operational amplifier 176 has the effectof causing integration across the capacitor 178 to establish an outputsignal 180 at a voltage level near the ground reference. A voltage levelnear the ground reference constitutes a logic low signal. Thus, in thenormal position of the switch 164, the output signal 180 from theintegrator circuit 179 is at a logic low level.

In response to the control signal 166 moving the switch 164 from itsnormal position shown in FIG. 7 to its activated position which is thealternate of that position shown in FIG. 7, the logic high triggersignal 120 is applied through the resistor 174 to the negative inputterminal of the operational amplifier 176. So long as the trigger signal120 is at the logic high level, the output signal 180 from theoperational amplifier 176 remains at a logic low level. However, becauseingress noise typically has the effect of rapidly subsiding ininstantaneous power, the instantaneous power will usually not exceed thethreshold for a significant sustained amount of time, thereby causingthe signal 120 to assume a logic low level during the time that theone-shot timer 162 supplies the control signal 166. Consequently, withthe switch 164 in the activated position and the signal 120 at a logiclow level, the operational amplifier 176 integrates this change of inputsignal level across the capacitor 178, which causes the output signal180 to start increasing from the ground reference level. If theinstantaneous power of the ingress noise remains low for a significantportion of the time that the one-shot timer 162 asserts the controlsignal 166, as is typical with ingress noise having an initialmomentarily-high instantaneous power burst, the voltage across thecapacitor 178 will increase to a level which corresponds to a logic highlevel of the signal 180.

The logic high output signal 180 is applied to one input terminal of anAND gate 167. The control signal 166 is applied to another inputterminal of the AND gate 167. The input terminal to which the controlsignal 166 is applied is an inverting input terminal, thereby causingthe AND gate 167 to respond to the inverted logic level of the controlsignal 166. The signal 180 remains at a logic high level for a timeperiod after integration ceases from the integration circuit 179, andthe control signal 166 assumes the logic low level at the end of theintegration time established by the one-shot timer 162. At that point,the AND gate 167 responds to two logic high signals (the logic lowsignal 166 is inverted at the input terminal), resulting in a logic highlevel signal 169 applied to an OR gate 182. The OR gate 182 supplies alogic high level signal 184 to a reset terminal of the latch 176. Thelatch 176 resets, and de-asserts the control signal 126 to the switches104 and 130, thereby closing the upstream communication path through theupstream filters 102 and 134. Thus, soon after the initial instantaneouspower of the ingress signal diminishes and the integration time set bythe one-shot timer 162 expires, the upstream communication path isclosed to the further conduction of upstream signals, thereby preventingany further ingress noise from entering the CATV network.

During the time and situation just described, another AND gate 185 hasno effect on the functionality. The signal 170 supplied by the one-shottimer 168 is asserted for a considerably longer period of time than theone-shot timer 162 asserts the control signal 166. The time of assertionof the signal 170 is the length of time, plus a margin for componenttolerances, of the longest single valid upstream packet or signalpermitted under the signal communication protocol. The time ofintegration represented by the assertion of the control signal 166 isconsiderably less than the longest single valid upstream packet. Duringthe integration of the instantaneous power of the ingress noise over thetime duration of the control signal 166, the output signal 170 is at alogic high level, the control signal 126 is at a logic high levelbecause the latch 172 will have been set by the trigger signal 120,before the signal 120 assumes a logic low level after the initial highinstantaneous power of the ingress noise has dissipated. The inputterminals of the AND gate 185 to which the signals 120 and 170 areapplied are inverting. Thus, under these conditions, the AND gate 185supplies an output signal 187 at a logic low level.

The situation of terminating the upstream communication path created bya burst of ingress noise before expiration of the time duration of amaximum-length valid upstream signal or packet is illustrated by thewaveform diagrams shown in FIG. 8, taken in connection with FIG. 7. Theingress noise signal is shown at 106. The instantaneous power of theingress noise exceeds the threshold power level and causes a logic hightrigger signal 120 from the comparator 112 at time point 148, therebytriggering the one-shot timers 162 and 168 and causing the controlsignals 166 and 170 to be asserted at the time point 148. The controlsignal 126 from the latch 172 also assumes a logic high level at timepoint 148 because the logic high trigger signal 120 sets the latch 172.The electronic switches 104 and 130 assume their activated positions forthe duration of the logic high control signal 126 to maintain theupstream communication path. At time point 150, the instantaneous powerof the ingress noise falls below the threshold power level, and thetrigger signal 120 assumes a logic low level. However, the firstone-shot timer 162 has not timed out and continues to deliver thecontrol signal 166 until it times out at time point 188. The timeduration between time points 148 and 188 is the time constant of theone-shot timer 162 which establishes the time duration of integration.The time for integrating a valid upstream signal is the time betweentime points 148 and 188.

If the integrated value indicates an upstream signal of unsustainedinstantaneous power, consistent with ingress noise that rapidlydissipates, the resulting logic high signal 180 from the integrator 179is applied to the OR gate 182. The OR gate 182 supplies the logic highsignal 180 at time point 188 which, when logically anded with thelogical inversion of signal 166, causes the AND gate 167 to assert thesignal 169. The OR gate 182 responds by asserting a logic high signal184, which resets the latch 172, thereby de-asserting the control signal126. The upstream communication path is terminated when the switches 104and 130 assume their normal positions.

As is understood from FIG. 8, the upstream communication path remainsopen from time point 148 to time point 188. This time is considerablyless than the maximum time length of a single valid upstream packet orsignal, represented by the time between points 148 and 189, or betweentime points 148 and 150 (FIG. 6). Consequently, even though the upstreamcommunication path is immediately established to allow upstream signalcommunication whenever the instantaneous power exceeds the threshold,that upstream communication path is closed to further upstreamcommunication very rapidly thereafter if spurious ingress noiseestablished that communication path.

Whenever an upstream signal has sustained instantaneous power, the noisemitigation circuit 160 assures that the upstream signal will beconducted to the CATV network. Such circumstances indicate a validupstream signal. As understood from FIG. 7, the trigger signal 120 isasserted at a logic high level when the valid upstream signal exceedsthe threshold. The latch 172 is set and asserts the logic high controlsignal 126 which moves the switches 104 and 132 their activatedpositions to establish the upstream communication path. The timers 162and 168 are triggered, and the one-shot timer 162 moves the switch 164to its activated position. The output signal 180 remains at a logic lowlevel during the time of a valid upstream signal while the one-shottimer 162 asserts the control signal 166 and while the logic hightrigger signal 120 remains at a logic high level due to the sustainedinstantaneous power of the valid upstream signal exceeding thethreshold. The logic low signal 180 and the inversion of the logic highsignal 166 at the input terminal of the AND gate 167 causes the AND gate167 to assert a logic low signal 169, which has no effect on the OR gate182 or the latch 172. Thus, during the transmission of a valid upstreamsignal, the AND gate 167 has no effect on the status of the latch 172.

On the other hand, the time constant of the one-shot timer 168 isconsiderably longer than the time constant of the one-shot timer 162.The signal 170 from the timer 168 is asserted for the time duration of asingle valid maximum-length upstream packet or signal. The logic highlevel of the signal 170 is inverted at the input terminal of the ANDgate 185. At this time, the control signal 126 is at a logic high levelbecause the latch 172 has been set. The continuous instantaneous powerof the valid upstream signal is represented by a logic high level of thetrigger signal 120. The logic high level of the signal 120 is invertedat the AND gate 185. The logic level of the signals applied to the ANDgate 185 causes it to supply a logic low signal 187, which has no effecton the latch 172 during conditions of sustained instantaneous power fromthe valid upstream signal.

When the valid upstream signal terminates, the logic high level of thesignal 120 changes to a logic low level. The logic low level signal 120is inverted at its input terminal to the AND gate 185. The logic highsignal 170 is still asserted by the one-shot timer 168, because thetimer 168 times the duration of a single valid maximum-length upstreamsignal. Until the one-shot timer 168 de-asserts the signal 170, the ANDgate 185 will not assert a logic high signal 187. However, when thesignal 170 is de-asserted, the AND gate 185 applies the logic highsignal 187 to the OR gate 182. The OR gate 182 asserts the signal 184 toreset the latch 172, and the control signal 126 is de-asserted. Theswitches 104 and 132 move to their normal positions and terminate theupstream communication path through the filters 102 and 134.

In response to sustained instantaneous power representative of a validupstream signal, the noise mitigation circuit 160 assures that anupstream communication path will be established for the maximum timeduration of a single valid upstream signal, provided that there issufficient instantaneous energy in the upstream signal during theintegration time established by the signal 166. In this manner, thecircuit 160 is similar to the circuit 100 (FIG. 3) which assures thatthe upstream communication path remains established for the timeduration of a single valid maximum-length upstream signal or packet.However, unlike the circuit 100 (FIG. 3) the circuit 160 discriminatesbetween short-duration high instantaneous power ingress noise andcontinuous-duration high instantaneous power upstream signals andrapidly terminates the upstream communication path in response to theformer.

The situation of maintaining the upstream communication path in responseto sustained instantaneous energy of an upstream signal during theintegration time established by the time constant of the one-shot timer162, to allow adequate time for a single valid upstream packet ofmaximum duration to be transmitted, is illustrated by the waveformdiagrams shown in FIG. 9, taken in connection with FIG. 7. The upstreamsignal is represented by a packet having a time duration less than themaximum allowed time duration for single valid upstream packet as shownat 106. The instantaneous power of the upstream packet 106 exceeds thethreshold power level and causes a logic high trigger signal 120 fromthe comparator 112 at time point 148, thereby triggering the one-shottimers 162 and 168 and causing the control signals 166 and 170 to beasserted at the same time point 148. The control signal 126 from thelatch 172 also assumes a logic high level at time point 148 due to theassertion of the logic high signal 120. The electronic switches 104 and130 assume their activated positions for the duration of the logic highsignal 126 and establish the upstream communication path. At time point188, the first one-shot timer 162 times out and de-asserts the controlsignal 166. The time duration between time points 148 and 188establishes the time duration of integration.

During the time of integration, the instantaneous power of the singlepacket 106 continuously exceeds the threshold level. Consequently, theoutput signal 180 from the integration circuit 179 remains at a logiclow level, and the inversion of the control signal 166 at the AND gate167 maintains the output signal 169 in a logic low level. At time point188 when the one-shot timer 162 times out, the control signal 166assumes a logic low level, but the inversion of that logic low level atthe input terminal to the AND gate 167, coupled with the continuouslogic low level signal 180 continues to maintain the output signal 169at a logic low level. The logic low signal 169 does not change for theduration of the situation shown in FIG. 9. As a result, the AND gate 167has no effect on resetting the latch 172 in this situation.

During the time between points 148 and 188, the logic high controlsignal 126, the logic high trigger signal 120, which is inverted at itsinput terminal to the AND gate 185, and the logic high control signal170, which is also inverted at its input terminal to the AND gate 185,cause the output signal 187 from the AND gate 185 to remain at a logiclow level. Therefore, during this time between points 148 and 188, thesignal 187 from the AND gate 185 has no effect on resetting the latch172.

At time point 190 the packet 106 terminates. The instantaneous powerassociated with the packet 106 also terminates, causing the triggersignal 120 to achieve a logic low level. However, the one-shot timer 168has not yet timed out, so its output signal 170 remains at a logic highlevel until time point 189. The logic low level trigger signal 120 doesnot change the state of the AND gate 185. Consequently, the latch with172 remains set at time point 190.

When the one-shot timer 168 times out, at point 189, the control signal170 assumes a low logic level. The low logic signal 170 is inverted atits input terminal to the AND gate 185. The trigger signal 120previously assumed a logic low level at time point 190. The inversion ofthe signals 120 and 170 at the input terminals to the AND gate 185results in three logic high input signals to the AND gate 185, causingthe output signal 187 to assume a logic high level. The logic highsignal 187 is applied to the OR gate 182, and the output signal 184 fromthe OR gate resets the latch 172. Upon reset, the latch 172 de-assertsthe control signal 126 at time point 189, thereby closing the upstreamcommunication path through the filters 102 and 134 as a result of theswitches 104 and 130 assuming their normal positions.

Thus, as is understood from FIG. 9, a valid upstream signal of anyduration will exceed the minimum power threshold measured during theintegration time established by the one-shot timer 162, and as aconsequence, the latch 172 will continue to assert the control signal126 and maintain the upstream communication path through the filters 102and 104. The upstream communication path will be maintained for theduration of the time constant of the one-shot timer 168, during whichits output signal 170 is asserted at a logic high level. By maintainingthe upstream communication path during the time that the one-shot timer168 asserts the control signal 170, it is assured that all validupstream signals having a time length at least equal to the maximumlength of a single valid upstream signal will pass through the upstreamcommunication path. Consequently, none of the information contained in asingle valid upstream packet will be lost or truncated.

The upstream signal communication path remains established during thetime between the actual end of the valid upstream packet and the end ofa maximum-length valid upstream packet, represented by the difference intime between points 190 and 189, but that amount of time is relativelyshort and maintenance of the upstream communication path during thistime assures that a valid upstream signal packet of any length up to themaximum length will be transmitted without loss or truncation of any ofits information.

In addition to the previously described advantages of quickly closingthe upstream communication path after it was established by ingressnoise and of establishing the upstream communication path for themaximum length of a valid upstream signal, the noise mitigation circuit160 also has the capability of transmitting multiple sequential validdata packets, without loss or truncation of information. This situationcan be understood by reference to FIG. 10, taken in conjunction withFIG. 7.

The first valid upstream packet of the multiple sequence of validupstream packets, shown at 106 in FIG. 10, establishes the upstreamcommunication path due to its sustained instantaneous energy. Thisenergy is sustained during the integration time established by theone-shot timer 162. The control signal 166 is asserted at a high logiclevel until time point 188, and the control signal 170 is asserted at ahigh logic level until time point 189.

The instantaneous power of the sequence of multiple valid upstreampackets remains above the threshold level and the trigger signal 120remains asserted at a logic high level for the duration of that sequenceof packets until time point 193, when the instantaneous power of themultiple sequential upstream packets terminates. The one-shot timer 168does not time out until time point 189, at which point its output signal170 assumes a logic low level at time point 189. The low logic level ofthe control signal 170 is inverted at its input terminal to the AND gate185. However, at time point 189, the states of the input signals to theAND gate 185 result in the AND gate 185 supplying a logic low outputsignal 187. The logic low output signal 187 has no effect on the OR gate182 and the latch 172 remains set.

At time point 193, the instantaneous power of the sequence of multiplevalid upstream packets 106 falls below the threshold, causing thetrigger signal 120 to assume a logic low level. The logic low level ofthe signal 120 at time point 193 is inverted at its input terminal tothe AND gate 185, causing the AND gate to assert a logic high outputsignal 187. The logic high signal 187 causes the OR gate 182 to assertthe signal 184, thereby resetting the latch 172 and de-asserting thesignal 126. The switches 104 and 130 assume their normal positions,thereby terminating the communication path through the upstream signalfilters 102 and 134.

In this manner, the upstream communication path is maintained for theduration of the multiple sequential packets, represented by the timebetween points 148 and 193. However, after the last packet in themultiple sequential series of valid upstream packets ends, the upstreamcommunication path is closed to the further transmission of upstreamsignals, thereby preventing ingress noise from entering the CATVnetwork.

As has been described in conjunction with FIGS. 7-10, any upstreamsignal, whether a valid upstream signal or ingress noise, which hassufficient instantaneous power to exceed the threshold will immediatelyopen the upstream communication path through the filters 102 and 134. Inthis sense, the noise mitigation circuit 160 does not distinguishbetween a valid upstream signals and invalid ingress noise which mayhave sufficient energy to exceed the threshold. Not distinguishingbetween these signals assures that there is no delay in transmittingvalid upstream signals. A delay in transmitting valid upstream signalscould lose or truncate part of the information contained in those validsignals. However, once the upstream communication path has beenestablished, the sustained instantaneous power of the upstream signal isintegrated during the integration time established by the one-shot timer162, between time points 148 and 188. If the instantaneous power of theupstream signal is not sustained, as is the typical case with ingressnoise, the upstream communication path is terminated thereafter at timepoint 188. On the other hand, if the instantaneous power of the upstreamsignal is sustained during the integration time, as is the typical casewith a valid upstream signal of any duration, the upstream communicationpath is maintained for the maximum duration of a single valid upstreamsignal or packet, represented by the time between points 148 and 189. Inthis manner, an upstream communication path is assured for the timeduration necessary to transmit a single valid upstream packet of maximumtime duration established by the communication protocol. Again, no lossor truncation of information of any valid upstream packet is assured.Similarly, there is no loss or truncation of the information containedin a sequence of multiple valid upstream packets, even when the multiplesequential upstream packets have a time duration which exceeds themaximum time duration of a single valid upstream packet. The upstreamcommunication path remains open for the duration of the multiplesequential upstream packets, represented by the time between points 148and 193. However as soon as the instantaneous power represented by themultiple upstream sequential packets falls below the threshold, at timepoint 193, the upstream communication path is terminated to prevent anyingress noise from entering the CATV network at the conclusion of themultiple sequential upstream packets.

The benefit of the termination resistors 103 and 190 is their ability toavoid signal reflections, as understood from FIGS. 3 and 7. Theproclivity for high-frequency signals to reflect is related to theimpedance characteristic of the termination of the conductor whichconducts those signals and to the frequency of those signals, as is wellknown. For this reason, coaxial cables are typically terminated byconnecting a terminating impedance between the signal-carrying centerconductor and the surrounding reference plane shielding. The terminatingimpedance value should have a value equal to a characteristic impedancebetween the signal-carrying conductor and the reference plane shielding,to minimize signal reflections.

The values of the termination resistors 103 and 190 are selected toequal the characteristic impedance of the coaxial cables which form thedrop cables 38 (FIG. 2), and that value is typically 75 ohms. Matchingthe value of the termination resistors 103 and 190 to the characteristicimpedance of the coaxial cables minimizes the amount of signalreflection. Reflected signals combine with the incident downstreamsignals and cancel or degrade the downstream signals. Minimizing thesignal reflection maximizes the quality and fidelity of the downstreamsignals and enhances the quality of service provided from the CATVnetwork.

A further significant feature is the incorporation of a gas tube surgeprotection device 192 in the network interface device 10, as shown inFIG. 3. The gas tube surge protection device 192 is an integralcomponent and is permanently enclosed within the housing 12 (FIG. 1).The gas tube surge protection device 192 provides protection againstdestruction of and damage to the components of the interface device 10which typically might arise from lightning strikes to the CATV network20 or from other unanticipated high voltage and high currentapplications to the CATV network. Because the infrastructure of the CATVnetwork extends over a considerable geographical area, a lightningstrike or other unexpected high voltage, high current application mayadversely affect or destroy electronic components in the CATV networkinfrastructure, including the interface devices 10. For this reason,industry standards require some form of surge protection.

The typical previous types of surge protectors are inductor-capacitorcircuits, metal oxide varistors, and avalanche diodes. These devices maybe made a part of a network interface device, or these devices areincluded in cable taps 36 (FIG. 2). Inductor-capacitor circuits, metaloxide varistors and avalanche diodes only offer effective protectionagainst relatively lower voltage and lower current surges.Inductor-capacitor circuits, metal oxide varistors and avalanche diodesare susceptible to failure in response to higher voltage and highercurrent surges, such as those arising from lightning strikes. Of course,the failure of such devices eliminates any protection and usually leadsto failure of the components within the CATV network and within thenetwork interface device. The CATV service provider is required toreplace failed network interface devices, but a failed surge protectormay not be recognized until after the destruction of other componentshas occurred.

Grounding blocks are another previous form of surge protection.Grounding blocks are devices used in cable taps 36 (FIG. 2), and includeconductors which provide a common ground reference among the variousdevices within the cable taps 36. Grounding blocks may also be used inconnection with a gas tube surge protection device within the cable taps36, but gas tube surge protection devices are not commonly used withgrounding blocks because of the relative expense associated with suchdevices and the perceived satisfactory protection available from thecommon grounding connection. The other disadvantage of using a gas tubesurge protection device with a grounding block is that the arrangementis not fully effective. The gas tube surge protection device is locatedat the cable taps 36 (FIG. 2), but the cable taps 36 are separated bydrop cables 38 from the network interface devices 10. A lightning strikeor other surge condition unexpectedly applied to one of the drop cables38 will be conducted directly to the interface device 10 which has nosurge protection, as well as to the cable tap 36. Any protectionprovided by the grounding block, whether or not it includes a gas tubesurge protection device, is not assuredly available to the networkinterface device 10, because the adverse surge can be conducted directlyto the network interface device 10 and avoid the gas tube surgeprotection device in the cable tap 36.

Incorporating the gas tube surge protection device 192 in the networkinterface device 10, as shown in FIG. 3, offers a greater capability toprotect against higher voltage and higher current surges and againstrepeated surges. The gas tube surge protection device 192 remainsfunctional in response to higher voltage and higher current surges thancan be responded to by inductor-capacitor circuits, metal oxidevaristors and avalanche diodes. The gas tube surge protection device 192also offers a capability to resist a greater number of multiple surgescompared to other known previous devices. While the previous devices mayrespond to a moderate number of moderate level surges, the number ofsuch responses is limited. After that number is exceeded, such previousdevices tend to fail even in response to moderate surge conditions.

Locating the gas tube surge protection device 192 in the networkinterface device 10 provides the best level of protection against highvoltage and high current surges arising within the CATV networkinfrastructure and arising from active and passive subscriber equipmentconnected to the network interface device 10. Downstream surges will besuppressed as they enter the network interface device 10 from the CATVnetwork infrastructure. Even though it is unlikely that a surgecondition will originate at the subscriber equipment connected to theinterface device 10, the gas tube surge protection device 192 willprovide protection for the other components within the CATV network 20from upstream surges.

Incorporating the gas tube surge protection device 192 in the networkinterface device 10 also offers economic advantages, which aretranslated into a lower cost to the CATV service provider. The increasedcost arising from incorporating the gas tube surge protection device 192in the network interface device 10 is more than offset by avoiding thenecessity to occasionally replace entire failed network interfacedevices and/or other components within the CATV network infrastructure.A gas tube surge protection device which is satisfactory for use in thenetwork interface device is part number BAS230V supplied by CITEL INC,of Miami, Fla., USA.

As described above, there are numerous advantages and improvementsavailable from the present invention. The upstream noise mitigationcircuits (100 and 160, FIGS. 3 and 7) respond to the instantaneous powerof upstream signals. When the instantaneous power exceeds apredetermined threshold, a signal path for conducting the upstreamsignal to the CATV network is immediately established. Establishing theupstream communication path immediately when the instantaneous power ofthe upstream signal exceeds the threshold substantially reduces ordiminishes the risk that information contained in the upstream signalwill be lost, truncated or diminished. The risk of truncating or losinginformation in the upstream signal is considerably reduced or diminishedcompared to devices which integrate the power of the upstream signalover a time period before establishing the upstream communication path.By responding to the instantaneous power, the information in validupstream signals is preserved. On the other hand, the upstream noisemitigation circuits 100 and 160 (FIGS. 3 and 7) offer the capability ofquickly isolating and terminating the upstream communication path andthereby minimizing the ingress noise entering the CATV network.

In addition, the incorporation of the gas tube surge protection devicewithin the network interface device itself offers substantial protectiveand economic advantages over the previous known uses of surge protectiondevices for CATV networks.

Many other advantages and improvements will be apparent upon gaining acomplete appreciation for the present invention. The preferredembodiments of the invention and many of its improvements have beendescribed with a degree of particularity. This detailed description isof preferred examples of implementing the invention and is notnecessarily intended to limit the scope of the invention. The scope ofthe invention is defined by the following claims.

1-20. (canceled)
 21. A noise-mitigation device for connecting subscriberequipment to a cable television (CATV) network, the device comprising:an input port configured to be connected to the CATV network; at leastone subscriber port configured to be connected to a subscriber device; adownstream signal path configured to transmit a downstream signal fromthe input port to the at least one subscriber port, wherein thedownstream signal path comprises at least one filter configured tofilter signals in an upstream frequency band; and an upstream signalpath configured to transmit an upstream signal from the at least onesubscriber port to the input port, wherein the upstream signal pathcomprises a noise mitigation circuit comprising: an upstream signalfilter configured to filter signals in a downstream frequency band thatis different from the upstream frequency band; at least one switchcoupled to the upstream signal filter, the at least one switch having anactive state and a default state, wherein, in the active state, the atleast one switch is configured to permit the upstream signal to pass,and in the default state, the at least one switch is configured to blockthe upstream signal from passing; a detector configured to determinewhether the upstream signal has a power level that is above a powerthreshold; and a first timer configured to expire after a first durationthat is at least equal to a maximum time for a data packet to passthrough the upstream signal path, wherein the noise mitigation circuitis configured to move the at least one switch to the active state andsubstantially simultaneously initiate the first timer at least partiallyin response to the detector determining that the power level is abovethe power threshold, and wherein the noise mitigation circuit is furtherconfigured to set the at least one switch in the default state at leastpartially in response to the first timer expiring and the detectordetermining that the power level is below the power threshold.
 22. Thedevice of claim 21, wherein the power threshold is adjustable.
 23. Thedevice of claim 21, wherein the upstream signal path further comprises asecond timer configured to expire after a second duration that is lessthan the first duration, wherein the noise mitigation circuit is furtherconfigured to: initiate the second timer when the detector determinesthat the power level of the upstream signal is above the powerthreshold; determine that the power level of the upstream signal isbelow the power threshold when the second timer expires; and set the atleast one switch to the default state at least partially in response tothe detector determining that the power level of the upstream signal isbelow the power threshold, prior to expiration of the first duration.24. The device of claim 23, wherein: the detector comprises a comparatorand a log amplifier detector; the log amplifier detector is configuredto provide a signal representative of the power level of the upstreamsignal to the comparator; the comparator is configured to compare thepower level of the upstream signal, as represented by the signal fromthe log amplifier detector, with the power threshold; and the comparatoris further configured to provide a comparator signal representing thatthe upstream signal is noise when the power level is below thethreshold.
 25. The device of claim 24, wherein the noise mitigationcircuit further comprises: an integrator circuit configured to integratethe comparator signal, so as to provide an integrator signalrepresentative of whether the upstream signal is transient noise that isabove the power threshold, wherein the integrator circuit is configuredto integrate the comparator signal in response to initiation of thesecond timer; and a latch having an output that is connected to the atleast one switch, wherein the at least one switch is configured to beset in the active state when the latch provides an active signal theretofrom the output, and in the default state otherwise, and wherein thelatch comprises: a set node configured to activate when the comparatorsignal represents that the signal is above the power threshold; a resetnode configured to activate when either or both of: the integratorsignal represents that the upstream signal is transient noise, and thesecond timer is expired; or the latch provides the active signal to theat least one switch, the first timer is expired, and the comparatorsignal indicates that the upstream signal is below the power threshold,wherein the latch is configured to provide the active signal when theset is activated, until the reset is activated.
 26. A noise-mitigationdevice for connecting subscriber equipment to a cable television (CATV)network, comprising: a detector configured to determine a power level ofan upstream signal, determine whether the upstream signal is noise basedat least partially on a comparison of the power level to a powerthreshold, and provide a detector signal representing that the upstreamsignal is not noise; a first timer connected to the detector, the firsttimer being configured to expire a first time duration after the firsttimer is initiated, wherein the first timer is configured to beinitiated when the detector provides the detector signal to the firsttimer; and at least one switch connected to the detector and to thefirst timer, wherein the at least one switch is configured to have anactive state that allows the upstream signal to pass through an upstreamsignal path of the device, and a default state that blocks the upstreamsignal from passing through the upstream signal path, wherein the atleast one switch is configured to be in the active state at leastpartially in response to the detector providing the detector signal, andto be in the default state after the first timer duration expires. 27.The device of claim 26, further comprising: an input port configured tobe connected to the CATV network; and at least one subscriber portconfigured to be connected to a subscriber device, wherein the upstreamsignal path extends from the at least one subscriber port to the inputport, and wherein the first time duration is at least equal to a maximumduration for a data packet to pass through the upstream path.
 28. Thedevice of claim 27, further comprising a downstream signal pathextending between the input port and the subscriber port, wherein: thedownstream signal path comprises one or more downstream filtersconfigured to filter signals outside of a downstream frequency band, theupstream signal path comprises one or more upstream filters configuredto filter signals outside of an upstream frequency band, and theupstream frequency band and the downstream frequency bands arenon-overlapping.
 29. The device of claim 26, further comprising a secondtimer configured to expire a second time duration after initiation ofthe second timer, the second time duration being less than the firsttime duration, wherein: the second timer is configured to initiatesubstantially simultaneously to the first timer being initiated; thedetector is configured to again determine whether the upstream signal isnoise based at least partially on a comparison of the power level of theupstream signal to the power threshold, in response to the second timerexpiring; and the at least one switch is configured to be set to thedefault state at least partially in response to the detector determiningthat the upstream signal is noise after the expiration of the secondtimer and before the expiration of the first timer.
 30. The device ofclaim 29, wherein: the detector comprises a comparator and a logamplifier detector; the log amplifier detector is configured to providea signal representative of the power level of the upstream signal to thecomparator; the comparator is configured to compare the power level ofthe upstream signal, as represented by the signal from the log amplifierdetector, with the power threshold; and the comparator is configured toprovide a comparator signal representing that the upstream signal isnoise when the power level is below the threshold.
 31. The device ofclaim 30, further comprising an integrator circuit configured tointegrate the comparator signal, so as to provide an integrator signalrepresentative of whether the upstream signal is transient noise that isabove the power threshold, wherein the integrator circuit is configuredsuch that initiation of the second timer causes the integrator circuitto integrate the comparator signal.
 32. The device of claim 31, furthercomprising a latch having an output that is connected to the at leastone switch, wherein the at least one switch is configured to be in theactive state when the latch provides an active signal thereto from theoutput, and in the default state otherwise, and wherein the latchcomprises: a set node configured to activate when the comparator signalrepresents that the signal is above the power threshold; a reset nodeconfigured to activate when either or both of: the integrator signalrepresents that the upstream signal is transient noise, and the secondtimer is expired; or the latch provides the active signal to the atleast one switch, the first timer is expired, and the comparator signalindicates that the upstream signal is below the power threshold, whereinthe latch is configured to provide the active signal when the set isactivated, until the reset is activated.
 33. A noise-mitigation devicefor connecting subscriber equipment to a cable television (CATV)network, the device comprising: a first port configured to receive adownstream signal from the CATV network and to provide an upstreamsignal to the CATV network; a second port configured to receive thedownstream signal from the first port and to receive upstream signalfrom a subscriber device; and a circuit coupled to the first port andthe second port and configured to transmit the upstream signal from thesecond port to the first port, wherein the circuit is configured to:compare a power level of the upstream signal to a power threshold;communicate, for at least a transmission time duration, the upstreamsignal from the second port at least partially in response to the powerlevel of the upstream signal being above the power threshold, thetransmission time duration being at least equal to a time required for adata packet to be transmitted from the second port to the first port;and after the transmission time duration expires, block communication ofthe upstream signal from the second port to the first port.
 34. Thedevice of claim 33, wherein the power threshold is static.
 35. Thedevice of claim 33, further comprising a downstream path configured totransmit the downstream signal in a first, downstream signal frequencyband from the first port to the second port, and prevent transmission ofsignals outside of the first, downstream signal frequency band from thefirst port to the second port.
 36. The device of claim 35, furthercomprising an upstream path configured to transmit signals in a second,upstream data signal frequency band from the second port to the firstport, the second frequency band being different from the first frequencyband, wherein the circuit is part of the upstream path.
 37. The deviceof claim 33, wherein the circuit comprises: at least one switch in anupstream signal path from the second port to the first port, wherein theat least one switch has an active state in which the at least one switchis configured to allow the upstream signals to pass through the upstreamsignal path, and a default state in which the at least one switch isconfigured to block the upstream signal from passing through theupstream signal path; and a first timer that expires at the transmissiontime duration after the first timer is initiated, wherein the circuit isconfigured to: substantially simultaneously supply signals to at leastone switch, to move the at least one switch to the active state, and tothe first timer, to initiate the first timer, and move the at least oneswitch to the default state after expiration of the first timer.
 38. Thedevice of claim 33, wherein the circuit further comprises a first timerand a second timer, wherein: the first timer is configured to expire afirst time duration after initiation, the first time duration beingshorter than the transmission time duration; the second timer isconfigured to expire at a second time duration after initiation, thesecond time duration being substantially equal to the transmission timeduration; the first and second timers are configured to be initiated atleast partially in response to power level of the upstream signal beingabove the power threshold; and the circuit is configured to determinewhether the upstream signal is below the power threshold after the firsttimer expires, and to block signals from communicating from the secondport to the first port after the first timer expires and before thesecond timer expires at least partially in response to determining thatthe upstream signal below the threshold.
 39. The device of claim 38,wherein the circuit further comprises an integrator configured tointegrate the upstream signal during the first time duration afterinitiation of the first timer.
 40. The device of claim 33, furthercomprising: an active signal path comprising the circuit and the secondport; and a passive signal path extending from the first port andcomprising one or more passive ports, wherein the passive signal path isconfigured to transmit signals between the first port and the one ormore passive ports, and wherein the passive signal path is free frompowered devices.